Methods and systems disclosed herein relate generally to measuring fluid or gas flow, and more particularly to sensing cross-flow orientation and speed of a fluid over an extended range.
The wind direction of the atmosphere is routinely monitored by remote sensing techniques such as Light Detection and Ranging (LIDAR) and Sonic Detection and Ranging (SODAR). The measurement principles usually employed are the Doppler shift in applications where the flow is in the direction of the detecting beam (Benedetti-Michelangeli et al., Measurements of aerosol motion and wind velocity in the lower troposphere by doppler optical radar, J Atmos Sci 29, 906-910 (1972)) and cross-correlation of the scintillation pattern in a crosswind geometry (T. Wang, G. R. Ochs, and R. S. Lawrence, Wind measurements by the temporal cross-correlation of the optical scintillations, Appl Optics 20, 4073-4081 (1981)).
Scintillometers are used for cross wind measurements over extended ranges. Most applications for this kind of measurement are found in meteorology, climate, and environmental sciences. Monitoring the flow (wind in case of the atmosphere) is important to understand the transport of heat, gases, nutrients, and other substances which affect the environment. Also the wind speed over airport runways is sometimes monitored remotely by dual large-aperture scintillometers (DLAS) or single large-aperture scintillometers (SLAS). Similar instruments are being used to survey the wind conditions at potential sites for wind farms. Cross-correlation of the scintillation between two beams is utilized to determine the flow direction (e.g. DLAS). SLAS on the other hand only provide information on the speed of the flow, but lack the ability to determine the flow direction.
What is needed is a method that relies on the beam wander (also referred to herein interchangeably as wander, beam deflection, or deflection) of a single laser beam, measured in two orthogonal directions, to infer the cross-flow direction of an optically active turbulent medium. What is further needed is a system for remotely sensing the cross-flow orientation of a fluid (including a gaseous fluid) over an extended range.